This invention relates to a method of manufacturing wiring device for mounting electronic components and, more particularly, to a method of manufacturing thick-film circuit device.
In order to mount electronic components such as semiconductor elements directly on a circuit device, ceramic substrates on which passive components and their interconnections are deposited in the form of a thick or thin film are commonly used. With the recent advancement of computer techniques, circuit device having a higher density of circuit have come to be demanded. Conventionally, the thick-film technique is used for the manufacture of circuit device of relatively low density of circuit having a wire width of 100.mu. or greater, while the thin-film technique is used for the manufacture of circuit device of high density of circuit having a wire width of less than 100.mu.. The thick-film technique involves a printing process similar to stencil printing in which a circuit pattern is formed by depositing an electrically conductive or insulating paste for thick-film circuit through a fine mesh screen having a desired pattern baked thereon. This thick-film printing method is useful, as described above, for the formation of circuit patterns having a wire width of 100.mu. or greater, but has been found to have a number of disadvantages in forming circuit patterns with a smaller wire width. That is, the screen of commonly used type which consists of a mesh work made of fine stainless steel wire has certain limits imposed on the spacing of the meshwork and the thickness of the stainless steel wire, because of the strength requirements for the screen. Thus, the presence of the screen itself constitutes a serious obstacle as the wire width of the circuit pattern to be printed is reduced to a minimum. For example, when the wire width is reduced to a minimum, the fine dust trapped in the meshes of the screen may cut off the thick-film paste pattern, resulting in poor electrical connections. Or, the presence of the stainless steel wires of the screen may produce uneven wire widths and wire thicknesses of the printed circuit pattern, thereby forming a cause for variation of electrical characteristics.
On the other hand, the thin-film technique involves an evaporation or sputtering process by which an electrical material is deposited on a substrate through the openings previously formed with a photosensitive resin. This technique can produce minute circuit patterns having a wire width of less than 100.mu., as contrasted with the thick-film technique. In these days, however, circuit devices have come not only to have a minimized wire width but also to include a plurality of layers comprising electrically conductive layers separated by electrical insulation layers. The thin-film technique has been found to be unsuitable for the formation of such electrical insulation layers. More particularly, since the thermal expansion coefficient of an electrical insulating material is much lower than that of a metal, the electrically insulating layers formed by evaporation or sputtering are in danger of being cracked. The thick-film technique using a paste for thick-film circuit is free from the above-described danger because the thermal expansion coefficient of the paste can be controlled. It is therefore necessary to rely upon the thick-film technique for the manufacture of large-sized, multi-layer circuit device measuring, for example, 80 by 80 mm. However, the above-described difficulties in forming circuit patterns with a wire width of less than 100.mu. and holes of small diameter have been an impediment to further densification.